The present invention relates to a funnel used for a cathode ray tube, and specifically relates to a funnel for a cathode ray tube, on an inner wall of a side wall portion of which an anode button is sealed for mounting a getter mounting body and protrusions are formed for restricting a turn of the getter mounting body around the anode button.
As is well known, a cathode ray tube includes a panel on which an image is projected, a funnel, and a neck tube in a tube shape with a small diameter as principal glass parts. As shown in FIG. 5, a funnel 1 is provided with a side wall portion 4 which is gradually decreasing in diameter in a direction from a seal edge surface 2 provided for sealing the panel toward a neck tube 3. An anode button 6 is sealed and embedded at a predetermined position on an inner wall 5 of the side wall portion 4. Frit glass is used for fusing to join the seal edge surface 2 of the funnel 1 to a seal edge surface of the panel in a manufacturing process for the cathode ray tube, and this process seals the panel to the funnel 1.
The funnel 1 is molded such that high temperature molten glass gob is supplied to a mold comprising a bottom mold and a shell mold, in this state, a plunger is pressed against the gob to apply a pressing force, thereby, the molten glass gob moves up to a part corresponding to the side wall portion 4 in a direction toward the seal edge surface 2 while the molten glass gob is pressed and extended.
On the other hand, in the manufacturing process for the cathode ray tube after molding the funnel 1, the inside of the cathode ray tube is evacuated after the funnel 1 is sealed to the panel, a high frequency irradiation from the outside of the cathode ray tube heats and vaporizes getter 7 such as barium held on the inner wall 5 of the funnel 1, the getter 7 reacts with a small amount of residual air remaining inside the cathode ray tube, and thereby the vacuum increases to about 10xe2x88x926 Pa.
As means for holding the getter 7 on the inner wall 5 of the funnel 1 in a preceding process, the getter 7 is mounted to one end of an elastic metal piece 8, which serves as a mounting member, to form a getter mounting body 10, the elastic metal piece 8 is attached to the anode button 6 sealed and embedded on the inner wall 5 of the side wall portion 4, and an elastic force of the elastic metal piece 8 presses the getter 7 against the inner wall 5 of the side wall portion 4. When the elastic metal piece 8 is attached to the anode button 6, a protruding terminal in a spherical or cylindrical shape formed on the anode button 6 is engaged with an engaging hole 8a formed through the elastic metal piece 8.
The elastic force of the elastic metal piece 8 to which the getter 7 is attached simply allows the anode button 6 to support the elastic metal piece 8. When a mechanical vibration acts during transporting or handling the cathode ray tube, the elastic metal piece 8 turns around the anode button 6, and the position of the getter 7 is displaced from a desired initial position.
As a result, when the high frequency heating is performed on the getter 7 from the outside of the cathode ray tube after the panel is sealed to the funnel 1, because the target is so displaced that the heating and vaporizing of the getter is obstructed, an inner atmosphere in the cathode ray tube does not reach required high vacuum, and defective emission of the electron beam, and consequently, a degraded picture receiving characteristic are generated. In this case, because the inside of the cathode ray tube is evacuated, it is extremely difficult to adjust the getter position, and consequently it becomes impossible to apply the cathode ray tube to a practical use.
To solve this problem, Japanese Utility Model Laid-Open Publication No. Hei. 3-8855 discloses a technology wherein a pair of protrusions made of glass-buildups are formed on the inner wall 5 of the funnel 1. Namely, a pair of the protrusions 9 are formed in a neighborhood of the anode button 6 on the inner wall 5 so as to clamp the elastic metal piece 8 from the both sides, and the existence of the pair of protrusions 9 prevents the getter mounting body 10 from turning around the anode button 6.
However, prior art including the disclosed technology in the publication gives no consideration to the shape of the protrusions 9, and the protrusions 9 are simply formed just for preventing the turn of the getter mounting body 10. Specifically, as shown in FIG. 6, the conventional protrusions 9 are formed such that the most protruded part 9a on the basis of the inner wall 5 of the funnel 1 continues to the inner wall 5 at a side of the seal edge surface 2 through a first slope 9b, and the most protruded parts 9a continues to the inner wall 5 at a side of the neck 3 through a second slope 9c. The first slope 9b and the second slope 9c are set to the same inclination, namely the same slope angle, on the basis of the inner wall 5.
In this case, there is a large difference in flow speed between the molten glass flowing on parts corresponding to the protrusions 9 and the molten glass flowing on parts corresponding to the inner wall 5 in the neighborhoods of the protrusions 9, which are not protruded, when the molten glass moves up on the part corresponding to the side wall portion 4 toward the seal edge surface 2. When the two flows of the molten glass are different from each other in the flow speed and they merge together in the neighborhoods of the end parts at the side of the seal edge surface 2 corresponding to the protrusions 9, the flow of the molten glass is disturbed and obstructed in the neighborhoods of the end parts. As a result, in the molded funnel 1, a defective molding such as a wrinkle or a crack is generated in the neighborhoods of the ends of the protrusions 9 at the side of the seal edge surface 2.
In view of the foregoing, an object of the present invention is to improve the constitution of the protrusions formed on the inner wall of the funnel for preventing the turn of the getter mounting body, thereby to effectively smooth the flow of the molten glass in the neighborhoods of the protrusions when the funnel is molded, and to prevent the generation of the defective molding such as a wrinkle or a crack.
To attain the object above, the present invention provides a funnel for a cathode ray tube, comprising a seal edge surface provided for sealing a panel, a side wall portion gradually decreasing in diameter in a direction from the seal edge surface to a neck tube side, an anode button sealed on an inner wall of the side wall portion to which a getter mounting body comprising a getter and a mounting member is attached, and at least a pair of protrusions formed for restricting the getter mounting body from turning around the anode button from both sides, wherein each of the protrusions continues to the inner wall of the side wall portion as forming slopes from the most protruded part thereof toward the seal edge surface side and the neck tube side, and an inclination of the slope at the seal edge surface side is smaller than an inclination of the slope at the neck tube side.
With this constitution, because the inclination of the slope at the seal edge surface side is smaller than the inclination of the slope at the neck tube side for the most protruded parts of the protrusions, the following advantages are gained when the molten glass moves up on the part corresponding to the side wall portion toward the seal edge surface in the previously described process for molding the funnel. That is, even when there is a difference in the flow speed between the molten glass flowing on the part corresponding to the most protruded parts on the protrusions and the molten glass flowing on the part corresponding to the inner wall in the neighborhood of the protrusions, which are not protruded, one of the molten glass flows passes on the slopes at the seal edge surface side with the small inclination. Thereby, when it merges with the other of the molten glass flows during or after the passage, the difference in the flow speed between both of them properly decreases, and the directions of the flow of them become relatively similar. Thus, the situation where both of them disturb the mutual flows is restrained, and disturbance hardly occurs at the merging parts. As a result, a wrinkle or a crack is efficiently prevented from occurring in the neighborhoods of the ends of the protrusions at the seal edge surface side in the molded funnel.
In this case, the height of the most protruded part of the protrusion is set to a range of 0.5 mm to 1.5 mm, for example, on the basis of the inner wall. If the height is less than 0.5 mm, a proper turn preventing feature is not provided for the getter mounting body. If the height is more than 1.5 mm, the difference in the flow speed between the two flows of the molten glass is excessively large, and it is impossible to surely prevent the generation of the defective molding. And the inclination of the slope of the most protruded part at the seal edge surface side is set to a range of 2xc2x0 to 10xc2x0 on the basis of the inner wall, for example, and the slope at the neck tube side is set to a range of 7xc2x0 to 20xc2x0, for example. If the inclination of the slope at the seal edge surface side is less than 2xc2x0, the length of the slope toward the seal edge surface is excessively long. If it is more than 10xc2x0 disturbance occurs at the part where two flows of the molten glass merge, and it is impossible to surely prevent the generation of the defective molding. If the inclination of the slope at the neck tube side is less than 7xc2x0, sufficient height of the protrusion is not obtained, or the entire length of the protrusion from the neck tube side to the seal edge surface side is excessively long. If it is more than 20xc2x0, the slope prevents the flow of the molten glass, and another defective molding may occur in the neighborhoods of the ends of the protrusions at the neck tube side. The forms of the slopes at the seal edge surface side and the neck tube side may be a line or a high-order curve.
It is preferable that each of the protrusions further continues to the inner wall of the side wall portion as forming slopes from the most protruded part toward the getter mounting body side and the opposite side of the getter mounting body side, and an inclination of the slope at the opposite side of the getter mounting body side is smaller than an inclination of the slope at the getter mounting body side.
In this constitution, each of the protrusions comprises not only the slope from the most protruded part at the side of the getter mounting body, which opposes to the slope of the other protrusion disposed through the getter mounting body, but also the slope from the most protruded part at the opposite side of the getter mounting body. Thus, the flow of the molten glass all around the protrusions is smoothed, a temperature change caused by an excessive glass thickness change around the most protruded parts of the protrusions, and a resulting stress concentration are avoided when the funnel is molded, and it is possible to prevent the defective molding from occurring more surely. Further, because the inclination of the slope at the opposite side of the getter mounting body is set to smaller than that at the getter mounting body side, it is possible to efficiently prevent the defective molding from occurring while the turn preventing feature of the protrusions for the getter mounting body is properly secured. In terms of molding, it is preferable that curved surfaces with predetermined curvature radius be formed on bent parts where the slopes at the getter mounting body side and the opposite side of the getter mounting body from the most protruded part continue to the inner wall. It is preferable that a section shape obtained by cutting the protrusion in parallel with the inner wall be a shape whose width gradually decreases toward the opposite side of the getter mounting body, such as a shape close to a partial ellipse or a trapezoid.
Further, it is preferable that the protrusions be formed approximately symmetrically on both sides of a virtual baseline which passes through the center of the anode button and extends to the seal edge surface and the neck tube. With this constitution, a mutual positional relationship among the anode button and the individual protrusions is corrected, a geometrical deviation in attaching the getter mounting body to the anode button is eliminated, and a geometrical deviation in the state of the individual protrusions for preventing the turn of the getter mounting body (the clamping state) is restrained from occurring. As a result, the turn of the getter mounting body around the anode button is properly prevented.
It is preferable that each of the protrusions be formed such that a length thereof in a direction parallel with the virtual baseline is longer than a width in a direction perpendicular to the baseline. With this constitution, forming only the pair of the protrusions is possible to secure the length of the protrusions required for preventing the turn of the getter mounting body, and to decrease the width of the protrusions. As a result, the overall size and the number of the protrusions can be decreased, and consequently, the product cost can be reduced.
It is preferable that a side surface of the protrusion at the getter mounting body side be formed almost linear in a direction parallel with the virtual baseline. With this constitution, when the getter is circular, or the mounting member is rectangular, the protrusions surely clamp the getter mounting body. As a result, convenience increases, and the work for making the getter held on the funnel inner wall can be simplified.
It is preferable that the virtual baseline be an intersection between a virtual plane including a tube axis of the funnel and the inner wall of the side wall portion, and pass through approximately the center in a side direction of the seal edge surface. With this constitution, it is easy to design the shape of the protrusions, and to machine and manufacture the mold for the molding.